Various semiconductor devices use a voltage source selection circuit to select and output one of a plurality of input voltages. Among a more general class of voltage source selection circuits, a maximum voltage selection circuit is a circuit that selects a highest power supply voltage among a plurality of power supply voltages to ensure stable operation of a coupled device/circuit. For example, a maximum voltage selection circuit may be used to stably operate a power supply gate of a voltage boost circuit such as, for example, a DC-to-DC converter.
Conventional maximum voltage selection circuits, however, generally rely on an operational amplifier to compare the plurality of to-be selected power supply voltages, and operating such an operational amplifier requires using a dedicated bias circuit, which disadvantageously consumes additional power. Thus, conventional maximum voltage selection circuit are not entirely satisfactory.